Re: Programming style question

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From	"Jukka K. Korpela" <jkorpela@cs.tut.fi>
Newsgroups	comp.lang.javascript
Subject	Re: Programming style question
Date	Thu, 18 Oct 2012 15:32:39 +0300
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2012-10-18 15:06, Patricia Shanahan wrote:

 > Thomas 'PointedEars' Lahn wrote:
>
>> No.  (However, contrary to common misconception, there are no "untyped
>> variables".  Implementations of ECMAScript Ed. 1 to 3, 5, and 5.1 are
>> dynamically and weakly typed, not untyped.  Uninitialized variables
>> and trailing parameters for which no argument has been passed, hold
>> the `undefined' value, the sole value of the Undefined type.)

That's misleading play with words. Calling a variable typed just because 
its values have types is pointless.

> As I understand the issue, a variable always has a type, but that type
> can change on assignment.

No, a variable has values (possible different values, possibly of 
different types, at different times, and the values have types.

 > Similarly, the type of a formal parameter is
> determined by the type of the actual parameter in the call

A formal parameter has no type. Its values may have types. When you call 
foo(42), then the formal parameter gets the value 42, a number. When you 
call foo('a'), it gets the value 'a', a string. There is no point in 
confusing this by saying that parameters or variables have types.

As a programming style matter, you can decide to use each variable for 
values of a single type only. You can say that in a comment, or maybe 
just implicitly in initialization, e.g. var boo = '' would mean (in 
"typed style") that you intend to use boo with a string as its value.

I don't see any general problem with such an approach. It's mostly a 
good principle to use one variable for values of one type - one might 
even say that it's probably worth a comment in the source if you do 
otherwise in some case.

However, it is essential to note that the mechanisms of the language do 
not protect you from "type errors" in the sense as in many other 
languages where you get a compile-time or run-time message about 
assignment of a value of a wrong type. Neither do you get automatic type 
conversions based on the type of a variable - simply because variables 
do not have types in JavaScript.

-- 
Yucca, http://www.cs.tut.fi/~jkorpela/

Thread

Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 08:32 +0100
  Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-18 10:23 +0200
    Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:42 +0100
      Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-18 17:59 +0200
        Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-18 09:56 -0700
          Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-19 00:49 +0200
            Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-19 11:04 -0700
              Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 11:52 +0200
            Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-19 12:06 -0700
              Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-19 23:12 +0100
                Re: Programming style question "Mel Smith" <med_cutout_syntel@aol.com> - 2012-10-19 21:56 -0600
              Re: Programming style question Bart Van der Donck <bart@nijlen.com> - 2012-10-20 02:21 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 12:03 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-20 06:31 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 18:30 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-20 10:32 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-20 22:34 +0100
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-21 10:12 +0200
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-21 09:34 +0100
                Re: Programming style question Dr J R Stockton <reply1242@merlyn.demon.co.uk.invalid> - 2012-10-21 17:59 +0100
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-22 09:55 +0200
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-22 09:50 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-22 04:49 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-22 14:04 +0100
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-22 16:07 +0200
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-23 18:22 +0100
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-22 16:01 +0200
                Re: Programming style question Jim T. <x@y.z> - 2012-10-22 12:16 -0400
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-22 11:40 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-22 14:01 -0700
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:07 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-23 09:43 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-23 11:49 +0200
                Re: Programming style question Jim T. <x@y.z> - 2012-10-23 15:52 -0400
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-23 13:07 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-23 22:45 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-23 14:14 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-24 09:35 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-24 10:17 -0700
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-25 18:41 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-25 17:03 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-25 20:14 -0700
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-25 20:46 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-26 09:55 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-26 06:18 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-26 17:43 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-26 09:57 -0700
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-26 10:24 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-26 14:18 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 10:45 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 12:58 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 16:18 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 18:08 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 18:26 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 19:43 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 21:09 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 22:53 +0200
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-28 11:37 +0000
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-28 12:50 +0100
                Re: Programming style question Martin Leese <please@see.Web.for.e-mail.INVALID> - 2012-10-28 13:43 -0600
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-28 23:58 +0100
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-29 11:18 +0000
                Re: Programming style question Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2012-10-27 23:58 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-28 12:43 +0100
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-27 19:44 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-24 12:06 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 21:27 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-24 15:12 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-25 01:29 +0100
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-24 21:25 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 21:57 +0200
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-25 01:11 +0200
                Re: Programming style question Christoph Becker <cmbecker69@gmx.de> - 2012-10-25 02:00 +0200
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-24 20:27 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-25 08:44 +0200
                Re: Programming style question Adam Silver <adambsilver@gmail.com> - 2012-10-25 04:28 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-25 23:18 +0200
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-26 08:24 -0700
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-11-07 22:13 +0100
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-11-07 21:51 +0000
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-07 23:47 +0100
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-11-08 01:14 +0100
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-11-07 16:51 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 16:45 +0100
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-11-08 08:02 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 17:39 +0100
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-11-08 11:25 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 22:25 +0100
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-11-09 10:19 +0000
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-09 17:41 +0100
                Re: Programming style question Dr J R Stockton <reply1245@merlyn.demon.co.uk.invalid> - 2012-11-10 22:38 +0000
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-22 12:32 -0700
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:05 +0200
                Re: Programming style question Christoph Becker <cmbecker69@gmx.de> - 2012-10-22 22:11 +0200
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-23 02:42 +0200
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:08 +0200
              Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 18:34 +0200
  Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-18 11:57 +0200
    Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:06 +0100
      Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-18 15:32 +0300
        Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:37 +0100
          Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-18 15:55 +0300
          Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-19 10:12 +0100
            Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-19 07:24 -0700
              Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-20 17:47 +0100
          Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:15 +0100
            Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:31 +0100
            Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-24 07:34 +0300
              Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 19:57 +0200
                Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-24 21:02 +0300
        Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 20:15 -0700
      Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:21 +0100
  Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-21 17:57 -0700

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